The present invention relates to a wound healing process for treating Stages I and II human wounds that heal by secondary intention. Secondary intention means a healing by closure of a wound with granulations that form from the innermost base of the wound and proceed outwardly from the base and along the wound sides toward the surface of the wound. Secondary intention healing results in closure of the wound without closure by surgical intervention.
The classification of surface wound types by Stages is conventional. Four distinct stages are defined, primarily by their depth. A Stage I wound is a shallow wound that penetrates into but not through the epidermis. A stage II wound penetrates through the epidermis, and possibly into some subcutaneous tissue like fat, but not into muscle or bone. Examples of the Stages I and II wounds that often are healed by secondary intention include pressure sores, venus statis ulcers, and diabetic ulcers.
Prior art techniques and wound dressings for treating Stages I and II wounds have often extended, rather than reduced the time for healing. The ideal process for treating such dermal lesions provides many benefits, including maintaining tissue hydration at levels appropriate for the phase of wound healing, protecting against bacterial infiltration, eliminating premature scab formation, enhancing granulation, epithelial migration, and wound contraction and closing, all of which speed healing. To achieve these benefits, the process should provide the wound with a liquid and microorganism barrier, remove and prevent pooling of exudate while keeping the wound moist throughout most of the healing period, permit adequate oxygen ingress and carbon dioxide egress, and minimize trauma to surrounding and new tissue when removing the dressing.
Many prior art dressings provide some, but not all, of the above benefits. U.S. Pat. Nos. 4,598,004; 3,645,835; 4,638,797; 4,600,001; and 4,413,621 disclose wound dressings that are generally adequate for shallow wounds having low exudate levels. However, because of the low moisture vapor permeability rate (MVTR) of the dressings, they cannot remove exudate fast enough to prevent pooling under the dressing in applications to high exudate wounds.
Similarity the hydrogel dressings described in U.S. Pat. Nos. 4,554,317; 3,419,006; 3,993,551 and 3,664,343 have low exudate removal capabilities requiring frequent dressing changes.
To increase exudate removal, pouch dressings have been used, such as those described in U.S. Pat. Nos. 4,645,624; 4,499,896; and 4,657,006. These dressings effectively remove greater quantities of exudate, but are unable to manage the fluid of highly exudative wounds. Also these pouch dressings tend to separate from the skin prematurely.
Impermeable occlusive dressings have been used to give better adhesion and good absorption, as described in U.S. Pat. Nos. 3,972,328; and 4,538,603 and EP 0,190,814. These dressings comprise a layer of rubber based adhesive, compounded with absorbent material to absorb the exudate and retain it in the dressing. If not replaced frequently on highly exudative wounds, large quantities of exudate are entrapped next to the wound at a significant fluid pressure. Extensive skin macerations often occurs. Also the adherence of the dressings often fail, releasing entrapped fluid onto the patient.
U.S. Pat. Nos. 4,477,325 and 4,738,257 disclose occlusive rubber dressings, cross-linked to prevent degradation of the dressing into the wound during healing. Skin adhesion failures and leakage are not eliminated by these dressings.
To improve exudate management, and minimize the degradation of the dressing into the wound, island dressings have been used. As described in U.S. Pat. Nos. 4,561,435; 4,649,909 and 4,753,231, the island dressings absorb the exudate from the wound and evaporate it into the atmosphere through a water vapor permeable film These dressings do not manage exudate well for highly exudative wounds.
These and many other prior art dressings and healing methods have been described. However, not disclosed is a method incorporating the sequential use of dressings having different sequential moisture and as gas permeabilities to control the microenvironment of the wound to the conditions appropriate for healing during the particular phase of healing.
Healing of Stages I and II wounds, for purposes of the present invention, can be considered to take place in three phases. The phases are the same for Stages I and II, except in general the phases are longer time wise for Stage I.
There is a distinct optimal microenvironment for each healing phase that will produce the most rapid, quality healing. Sequentially the three phases are:
1. During phase 1, at the start of healing a Stage I or II wound, the wound exudes aqueous liquid, primarily blood and lymphatic fluid, at a rate of more about 5 ml per 24 hours. During the initial several days of healing, the most important factor is the removal of the exudate away from the wound. The optimum microenvironment enables the exudate to be drawn out of the wound as fast as it forms, readily pass through the dressing, and rapidly evaporate as it is exposed to the surrounding air. However, the exudate moisture is not removed so fast as to desiccate the wound. Also a high flow of oxygen from the outside air to the wound is necessary to promote new tissue growth, and carbon dioxide that forms in the wound area should readily pass to the outside air. The first phase continues until angiogenesis has begun to restore blood flow to the wound. Normally this requires about 5-15 days depending on the nature and location of the wound.
2. During phase 2 the wound size diminishes i.e. to about half the original size, angiogenesis continues restoring blood flow to the wound; and fibroblast migration and proliferation begin collagen generation and basement growth. For optimum 2nd phase healing, a high oxygen level, moist microenvironment is desired. The exudating of liquid decreases, normally to about 2 to 5 ml per 24 hours. Exudate removal should be sufficient to prevent pooling, but insufficient to desiccate the wound. The second healing phase continues until re-epithelization and re-mottling of the wound surface begins, normally about 5-15 days. PA1 3. During phase 3 of healing re-epithelization is completed and wound approximation and closure takes place. Exudation decreases and then stops and the final scar tissue forms. The healing process is completed during phase 3. A high oxygen, low to dry moisture microenvironment is appropriate. PA1 (a) initially applying to the wound about every 2-7 days a first type wound dressing that is liquid and microorganism impermeable and has high moisture vapor transmission rate, or permeability (MVTR), and high oxygen permeability; and PA1 (b) thereafter applying to the wound about every 2-7 days, another type wound dressing that is liquid and microorganism impermeable and has low moisture vapor permeability (MVTR) and high oxygen permeability.